Ouch! I can imagine something like that happening to me…and I would not be happy. That is just ridiculous as anyone with common sense could see. But, I understand your quandary….lose all the money you have already paid, or pay the extra and go alone.
I suggest you do as many activities as you can, watch as many shows, eat enough for two, go on the shore excursions and try to get as much of your money’s worth as you can. Then contact someone with more authority on your return and try to get them to see sense and give a refund (especially as you are a frequent customer.) I feel sorry for your wife not being able to go though. I doubt I could go on a cruise alone.